1. Field of the Invention
The present invention relates to a transmitting system for a small-sized vehicle in which a crankshaft of an engine and an input shaft of a multi-stage transmission are connected to each other through a fluid transmitting means including a pump impeller leading to the crankshaft, and a turbine impeller leading to the input shaft, i.e., through a torque converter or a fluid coupling.
2. Description of the Related Art
Such transmitting system for small-sized vehicles is already known, as disclosed in, for example, Japanese Patent Application Laid-open No.57-69163.
In such known transmitting system, as disclosed in the. above Publication, the crankshaft of the engine and the input shaft of the multi-stage transmission are connected to each other only through the torque converter, so that a torque shock generated at the time of the starting the vehicle or during shifting is absorbed by a slipping action of the torque converter.
However, the known transmitting system suffers from the following drawbacks: The torque converter or the fluid coupling has a slipping function, but performs the transmission of a torque to certain degree, as long as power is input from the engine to the torque converter or the fluid coupling. Therefore, in the known system, at the time of starting the vehicle in which the transmission is switched over from a neutral position to a low or first-speed position, a creep phenomenon is produced in which power is transmitted to a driven wheel of the vehicle to certain degree, even if the engine is in an idling state. During traveling of the vehicle, the friction always occurs in switching and sliding portions of the transmission due to the transmitted torque. For this reason, there are inconveniences that the resistance to the switching of the transmission is large, and a large shifting load is required.
Accordingly, it is an object of the present invention to provide a transmitting system of the above-described type for a small-sized vehicle, wherein the creep phenomenon is eliminated, and the shifting operation of the transmission can be carried out lightly.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a transmitting system for a small-sized vehicle in which a crankshaft of an engine and an input shaft of a multi-stage transmission are connected to each other through a fluid transmitting means including a pump impeller leading to the crankshaft, and a turbine impeller leading to the input shaft, wherein the transmitting system includes a shifting clutch which is interposed between the crankshaft and the input shaft in a series relation to the fluid transmitting means.
It should be noted incidentally that the fluid transmitting means corresponds to a torque converter T in embodiments of the present invention.
With the first feature, during idling of the engine, the transmitting of power to the shifting clutch and the like can be cut off by controlling the shifting clutch to its OFF state irrespective of the presence of the fluid transmitting means, even in a low or first-speed position of the transmission, thereby preventing the creep phenomenon. During shifting, the transmission can be brought into an unloaded state by first controlling the shifting clutch to its OFF state irrespective of the presence of the fluid transmitting means, thereby conducting the shifting lightly without generation of a torque shock.
According to a second aspect and feature of the present invention, in addition to the first feature, the shifting clutch is constructed into an on and off type having no half-clutched or clutch-slipping area.
With the second feature, it is possible to avoid heating and wearing of friction portions due to a half-clutching or clutch-slipping condition to enhance the durability of the shifting clutch. Moreover, even if the shifting clutch is brought at a stretch from its OFF state to its ON state beyond the half-clutched or clutch-slipping area, the accompanying torque shock is absorbed by the slipping action of the fluid transmitting means and hence, the riding comfort cannot be hindered.
According to a third aspect and feature of the present invention, in addition to the second feature, a shifting clutch actuator operated to bring the shifting clutch into an OFF state is arranged, and the shifting clutch actuator is operated upon generation of output signals from an idling sensor for detecting the idling state of the engine and from a shifting sensor for detecting the shifting operation of the multi-stage transmission.
With the third feature, during starting of the vehicle or during a shifting operation, the turning-on and off operation of the shifting clutch can be conducted precisely, which can contribute to an enhancement in durability of the clutch.
According to a fourth aspect and feature of the present invention, in addition to the first feature, the shifting clutch comprises a multi-plate friction engagement means including a plurality of driving friction plates connected to an input side, and a plurality of driven friction plates laminated alternately with the driving friction plates and connected to an output side, a centrifugal mechanism which moves in response to an increase in rotational speed of the input side of a value equal to or higher than a predetermined value thereby to bring the multi-plate friction engagement means into an ON state, and a clutch turning-off mechanism which brings the multi-plate friction engagement means into an OFF state at the time of shifting of the multi-stage transmission even during operation of the centrifugal mechanism.
The multi-plate friction engagement means corresponds to a clutch outer 137, a clutch inner 138, driving friction plates 139, driven friction plates 140 and a pressure receiving ring 141; the centrifugal mechanism corresponds to a driving plate 135, centrifugal weights 143 and a pivot 144; and the clutch turning-off mechanism corresponds to a release cam 150, a stationary cam 152 and a clutch arm 153, all in a fourth embodiment of the present invention which will be described hereinafter.
With the fourth feature, during idling of the engine, the forward movement of the vehicle at a very low speed due to a creep phenomenon of the fluid transmitting means can be prevented by bringing the multi-plate friction engagement means into its OFF state by the centrifugal mechanism. Moreover, during shifting, the multi-plate friction engagement means can be brought into its OFF state to reliably eliminate the shifting shock.
According to a fifth aspect and feature of the present invention, in addition to any one of the first to fourth features, the torque capacity of the shifting clutch is set at a value equal to or larger than the torque capacity of the fluid transmitting means.
With the fifth feature, even in a fully loaded state, the slipping of the shifting clutch can be prevented, whereby the durability of the shifting clutch can be ensured.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.